Found it...."Just a reminder that this TQFP package (AU) has 2 more ADC's than the DIP package (P), but (Arduino) A6 and A7 are only analog inputs, they cannot be used for outputs - nor do they have any pull-ups on them."

OK, so I now understand that my Etherten almost looks, walks and quacks like a Uno - but not quite. There is this functional difference, and it's all down to the different chip package. Is there any known instance of these pins being used? Freetronics are clearly not that serious about them.

A6 and A7 were also available on the Arduino Mini and Arduino Nano (and presumably some of the other SMT-chip based third party boards.) But using them is not compatible with the "popular" Arduino boards (Uno and its predecessors), and actually using them has never caught on.

I am planning on making a Header file to include these pins ("A6,A7"). I was reading the schematic and found them open. 1K resistor should allow the two pins to be available. I will check with my oscilloscope before I use them.

A6 and A7 are floating pins. using open floating pins just needs a resistor value to them. and setup a library to set pin A6, A7 as input. If the floating pins are used it should be stated in doc or other documents related to their value as floating pin assignments.

A6 and A7 are floating pins. using open floating pins just needs a resistor value to them. and setup a library to set pin A6, A7 as input. If the floating pins are used it should be stated in doc or other documents related to their value as floating pin assignments.

A6 and A7 are 100% analog only pins and they are only available onboards with the surface mount version of the ATmega328.

Don't try to treat them as digital inputs.

Finally we get somewhere. I know they are analog pins. I am going to treat them kindly. I did however ask if they are reserved for other function or devices. I have seen pins like this left to float for debugging hardware/software issues. My concern is are they free to use, or involved in other devices not spoken about in the past.

Finally we get somewhere. I know they are analog pins. I am going to treat them kindly. I did however ask if they are reserved for other function or devices. I have seen pins like this left to float for debugging hardware/software issues. My concern is are they free to use, or involved in other devices not spoken about in the past.

ADC6 and ADC7 are not reserved for any other purpose, they are exactly like the other analog pins, except that they are only analog inputs (cannot also be used as digital pins) and they are only available with the 32-pin packages.